smom-dbis-138/docs/bridge/trustless/RELAYER_FEES.md

Relayer Fees Documentation

Overview

This document describes the relayer fee mechanism for the trustless bridge system. Currently, there are no relayer fees, but this document outlines potential fee structures for future implementation.

Current State

No Relayer Fees

• Relayers currently receive no fees
• Revenue: None
• Costs: Gas fees + bond capital
• Profitability: Dependent on future fee implementation

Proposed Fee Structure

Option 1: Percentage of Deposit

Structure:

• Fee: 0.1% of deposit amount
• Paid by: Recipient (deducted from bridge amount)
• Example: 10 ETH deposit → 0.01 ETH fee

Implementation:

uint256 relayerFee = (amount * relayerFeeBps) / 10000;
uint256 bridgeAmount = amount - relayerFee;

Option 2: Fixed Fee

Structure:

• Fee: Fixed amount (e.g., 0.001 ETH)
• Paid by: Recipient
• Example: All deposits → 0.001 ETH fee

Implementation:

uint256 relayerFee = fixedRelayerFee;
uint256 bridgeAmount = amount - relayerFee;

Option 3: Tiered Fee

Structure:

• Small deposits (< 1 ETH): 0.2% fee
• Medium deposits (1-10 ETH): 0.1% fee
• Large deposits (> 10 ETH): 0.05% fee

Implementation:

uint256 relayerFeeBps;
if (amount < 1 ether) {
    relayerFeeBps = 20; // 0.2%
} else if (amount < 10 ether) {
    relayerFeeBps = 10; // 0.1%
} else {
    relayerFeeBps = 5; // 0.05%
}
uint256 relayerFee = (amount * relayerFeeBps) / 10000;

Fee Recipient

Option 1: Relayer (Claim Submitter)

• Fee goes to relayer who submitted claim
• Incentivizes fast claim submission
• Simple implementation

Option 2: Fee Pool

• Fees collected in pool
• Distributed to relayers based on activity
• More complex but fairer

Option 3: Split

• 50% to relayer
• 50% to fee pool
• Balance individual and collective incentives

Implementation Considerations

Contract Changes

InboxETH.sol:

• Add fee calculation
• Add fee recipient tracking
• Update submitClaim to handle fees

Example:

uint256 public relayerFeeBps = 10; // 0.1%

function submitClaim(...) external payable {
    // Calculate fee
    uint256 fee = (amount * relayerFeeBps) / 10000;
    uint256 bridgeAmount = amount - fee;
    
    // Store fee recipient
    relayerFees[depositId] = RelayerFee({
        relayer: msg.sender,
        amount: fee
    });
    
    // Continue with claim submission using bridgeAmount
}

User Impact

• Recipients receive slightly less (fee deducted)
• Transparent fee structure
• Competitive with other bridges

Economics

Relayer Economics

With Fees:

• Revenue: Relayer fees
• Costs: Gas + bond capital
• Profit: Revenue - Costs

Example:

• Deposit: 10 ETH
• Fee: 0.01 ETH (0.1%)
• Gas: 0.001 ETH
• Bond: 11 ETH (locked)
• Net: 0.009 ETH profit (if no challenge)

User Economics

With Fees:

• Receive: Deposit - Fee
• Example: 10 ETH deposit → 9.99 ETH received
• Fee: 0.01 ETH (0.1%)

Recommendations

Phase 1: Optional Fees

• Implement fee mechanism
• Set fee to 0% initially
• Allow enabling via governance/multisig

Phase 2: Gradual Rollout

• Start with low fees (0.05%)
• Monitor relayer participation
• Adjust based on data

Phase 3: Optimization

• Analyze optimal fee rate
• Consider tiered structure
• Optimize for relayer incentives

References

• InboxETH Contract: contracts/bridge/trustless/InboxETH.sol
• Relayer Guide: docs/operations/RELAYER_GUIDE.md
• Economics: docs/bridge/trustless/ARCHITECTURE.md